Pain-related evoked potentials: a comparative study between electrical stimulation using a concentric planar electrode and laser stimulation using a CO2 laser.

Summary Objective To compare the pain-related evoked potentials (PREPs) obtained by superficial electrical stimulation using a concentric planar electrode to those obtained by CO 2 laser stimulation. Methods In 12 healthy subjects, PREPs, sympathetic skin reflexes (SSRs), motor reaction times (mRTs), and the conduction velocity (CV) of the recruited nerve fibres were assessed in response to electrical and laser stimulation. Results In response to superficial electrical stimulation, PREP latencies and mRTs were shorter, while PREP amplitude tended to be increased. By contrast, SSR amplitudes and latencies and estimated CVs of the stimulated nerve fibres did not differ between electrical and laser stimulation. Fifteen minutes after PREP recordings, the residual pain intensity and the degree of unpleasantness were higher for laser stimulation than for electrical stimulation. In addition, CO 2 laser stimuli induced dyschromic spots on the skin. For these reasons, all subjects declared that they would prefer superficial electrical stimulation rather than CO 2 laser stimulation if they had to perform PREPs again. Conclusions The estimated CVs of the recruited nerve fibres and the localized pinprick sensation felt by the subjects suggest that small-diameter fibres in the A-delta range, conveying “first-pain” information, were stimulated in response to superficial electrical stimulation as for laser stimulation. Superficial electrical stimulation using a concentric planar electrode could be a valuable alternative to laser stimulation for assessing PREPs in the practice of clinical neurophysiology.